-ENODEV ourselves because if
DEBUG_FS is not compiled in, all the debugfs utility functions will
become no-op.

Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Acked-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
2äíu™